The invention relates to a semiconductor accelerometer, and more particularly to a semiconductor accelerometer having a structure suitable for a measurement of electrical output characteristics and a method of testing electrical output characteristics thereof.
Semiconductor accelerometers have been used for the measurement of the acceleration caused by a shock of a movement of a body. FIGS. 1 and 2 illustrate a structure of the semiconductor accelerometer in the prior art. Such semiconductor accelerometers essentially includes a sensor substrate 1, an upper covering member 15 which overlays the sensor substrate 1 and a bottom covering member 16 which underlies the sensor body 1. The sensor substrate 1 is provided at its uncovered upper surface with a plurality of bonding pads 4. The sensor substrate 1 essentially comprises a frame, a mass 9, beams 8 provided at opposite ends of the mass for supporting the mass 9 and gauge resistors 10 provided on the beams 8. The semiconductor accelerometer has apertures 6 and 7 between the sensor substrate 1 and the both covering members 15 and 16 respectively thereby allowing the mass 9 to be oscillated in the vertical direction. The upper covering member 15 is formed at its upper surface with a sensor chip 21. The sensor substrate 1 is formed by techniques such as etching so as to make the beams 8 to be very thin. The upper and under covering members 15 and 16 prevent the mass 9 to have over amplitude of the oscillation by an over-shock. The gauge resistors 10 are formed by using photolithography.
With the operation of the accelerometer, when an acceleration in the vertical direction is applied to the accelerometer, the oscillation of the mass 9 is caused by the inertial resistance of the mass 9. The variation of the mass 9 causes the beams 8 to have a strain by which the resistivity of the each gauge resistor 10 is varied. The variation of the resistivity of the gauge resistors 10 is converted into electrical signals, and thus the magnitude of the shock, or the acceleration may be converted into electrical signals thereby resulting in an accomplishment of the measurement of the acceleration.
The accomplishment of the correct measurement performance requires the accelerometer to take a test of the electrical output characteristics. In the prior art, the test of the electrical output characteristics is accomplished by oscillating the accelerometer with a vibrator in which the sensor chip 21 is mounted to the vibrator to apply the acceleration, or shock to the mass 9. Thus, the sensor chip 21 is required to securely be mounted to the vibrator by using an adhesive or the like in order to prevent a resonant oscillation of the sensor chip 21 to be caused. The test of the electrical output characteristics also requires the sensor chip 21 to be either mounted or dismounted to the vibrator. The mount by use of the adhesive renders the mount and dismount of the sensor chip 21 to the vibrator inconvenient. In view of ability of the vibrator, it is difficult for the prior art to mount a number of sensor chips 21 to the vibrator. It is thus difficult to accomplish concurrent measurements of characteristics of a number of accelerometers.